My right breast droops and clearly isn't the same size as the other. What should be done to correct this? (Photo)

First, I would suggest getting an ultrasound to see if a seroma, excess fluid, is still present. It does appear to be larger in your photos. Second, that implant has bottomed out and needs to be tightened and uplifted from below. You might need an internal bra of mesh for better support. If no fluid is present, you will need to go smaller. I suspect you still have fluid from the size difference.

Sounds like there are a lot of things going on with your breast.
To start with we always need to see a complete set of proper before and after pictures to make an assessment regarding the outcome of someone surgery.
When referring to left and right, we always use the patience left side as the reference.
When you describe issues with one side versus the other, make sure you’re not referring to how you see the breast on the picture but your left side(the side where your heart is) and your right side.
It looks to me like your left implant is riding low and has begun to bottom out.
Most people have a left breast that sits slightly higher on the chest wall than the right.
This would be consistent with yours as a baseline and probably your preoperative pictures will show this.
Your left nipple sits higher than your right.
Size discrepancy is either a discrepancy in your baseline size, implant, size or you may have a chronic seroma. The left implant has bottomed out. You also have significant divergence on the left breast.
You can’t surgically correct breast divergence.
Size discrepancy can be adjusted with revision surgery and the bottom out implant on the left should probably be addressed.
Correcting bottomed out implants is not always easy or straightforward.
It may not be a bad idea to get a second opinion.
For second opinion, consultations come prepared bringing with you a complete set of proper before and after pictures, operative reports, and progress notes of all things done to your breast. The easiest way to do this is to request a complete copy of your medical record.
Best,
Mats Hagstrom, MD.